An air-cooled engine, such as a general-purpose air-cooled single-cylinder engine, having a cylinder block made of aluminum alloy die casting is provided with an air guide casing for guiding cooling air from cooling fins to a high-temperature section of the cylinder block, etc.
One example of such an air-cooled engine in which an air guide casing is attached to a cylinder block, which has been disclosed in Japanese Utility Model Provisional Publication No. 60-23210 (No. 23210/1985), is shown in FIGS. 10 and 11.
FIG. 10 is a partially sectional view in which a fan cover portion of an engine is cut away, and FIG. 11 is a sectional view taken along the line E--E of FIG. 10. In FIG. 10, reference numeral 01 denotes an air-cooled single-cylinder engine having an inclined cylinder, and 02 denotes a cylinder block for the engine 01. The cylinder block 02 is a product made of aluminum alloy die casting, in which a cylinder barrel 03 having a cooling fan, a crankcase 02a, and the like are integrated.
A cooling fan 09 rotationally driven by a crankshaft (not shown) is provided at the side of the cylinder barrel 03, and the cooling fan 09, the cylinder barrel 03, and a cylinder head 06 are covered by a fan cover 010 from the side.
The fan cover 010 is the integration of a housing 011 for covering the cooling fan 09 and an air guide cover 013 for covering the cylinder barrel 03 and the cylinder head 06. An air intake (not shown) is open at the center of the housing 011. Also, a shroud 015 made of sheet metal is joined in a contacting manner by welding etc. along the lower side portion of the air guide cover 013 from the housing 011. Thereupon, there is no gap between the shroud 015 and the fan cover 010, both elements being integrated.
The shroud 015 continuously forms an arcuate edge 016 of the cylinder block 02, which is formed so as to extend to the crankcase 02a side, and a straight edge 017, which is formed so as to extend throughout the cylinder barrel 03 side and the cylinder head 06 side.
The cylinder block 02 has a wall-shaped rib 05 over the range from the crankcase 02a to the cylinder head 06. The shroud 015 and the fan cover 010 are in contact with the rib 05, whereby a cooling air path on the upstream side of cylinder is formed.
In the conventional engine 01 configured as described above, the cooling air produced by the cooling fan 09 is concentrated and guided to the high-temperature cylinder barrel 03 and cylinder head 06 by the fan cover 010, by which the cooling air is allowed to flow in layers to increase the cooling performance.
However, the engine having the air guide casing construction relating to the prior art, as shown in FIGS. 10 and 11, has the following problems to be solved.
(1) Since the shroud 015 is made of sheet metal, noise occurs easily due to resonance with engine vibration.
Also, since the edge of sheet metal is in contact with the cylinder block 02 at the portion of the shroud 015, a gap is liable to develop at this contact portion, whereby the leakage of cooling air and vibrations occur easily.
(2) Since the fan cover 010, which is formed by integrating the shroud 015 with the housing 011 by welding, is fastened to the cylinder block 02 with bolts, the number of bolts used is large, so that the assembly man-hour as well as the working cost is increased.
(3) Since the whole of the fan cover 010 including the shroud 015 is made of sheet metal, the weight is high.
The present invention was made in view of the above situation. Accordingly, a first object of the present invention is to provide an air guide casing for an air-cooled engine, which is configured so that vibrations of the air guide casing including a fan cover can be reduced by minimizing the use of members made of sheet metal, and noises produced by the resonance with engine vibration or other causes can be prevented.
A second object of the present invention is to provide an air guide casing for an air-cooled engine, in which the number of bolts used and the working man-hour for welding etc. can be decreased to achieve a cost reduction, and moreover the weight can be decreased.
A third object of the present invention is to provide an air guide casing for an air-cooled engine, which is configured so that a gap developing at the attaching portion where the air guide casing is attached to a cylinder block can be eliminated, by which the leakage of cooling air and the amplification of vibrations due to the gap can be prevented.